(1) Field of the Invention
This invention relates generally to DC-to-DC converters and relates more specifically to charge pumps having doubler, inverter or half the input voltage.
(2) Description of the Prior Art
Generating energy efficient reduced supply voltages is key in modern audio systems to be able to generate lower supply voltages when low power consumption for audio playback is required. Amplifiers adjusting their supply voltages dependent upon the output signal are called “Class-G” amplifiers. Current solutions have a step-down and invert function with a single flying capacitor.
It is a challenge for the designers of charge pumps generating voltages including step-down, invert and doubler voltages requiring a minimum number of switches with one flying capacitor.
There are known patents dealing with charge pumps generating symmetrical voltages.
U.S. Patent (U.S. Pat. No. 5,550,728 to Ellis) discloses charge pump structures having a reservoir capacitor and a pump capacitor embedded in a switch network. Each of the switches in the network is formed as an MOS transistor having a gate, which defines an array of spaced apertures and a plurality of sources and drains each disposed beneath a different one of the apertures.
U.S. Patent Application Publication (US 2009/0039947 to Williams) discloses a multiple output DC-to-DC voltage converter using a new time-multiplexed-capacitor converter algorithm and related circuit topologies. One embodiment of this invention includes a flying capacitor, a first output node, a second output node, and a switching network. The switching network configured to provide the following modes of circuit operation: 1) a first mode where the positive electrode of the flying capacitor is connected to an input voltage and the negative electrode of the flying capacitor is connected to ground; 2) a second mode where the negative electrode of the flying capacitor is connected to the input voltage and the positive electrode of the flying capacitor is connected to the first output node; and 3) a third mode where the positive electrode of the flying capacitor is connected to ground and the negative electrode of the flying capacitor is connected to the second output node.
U.S. Patent Application Publication (US 2003/0179593 to Burt et al.) proposes a charge pump circuit configured for charging of parasitic capacitances associated with charge pump capacitors in a manner that minimizes voltage ripple. The charge pump circuit is suitably configured with an independent charging circuit configured for supplying the current needed to charge the parasitic capacitances, rather than utilizing the reservoir capacitor to supply the needed current. The independent charging circuit can be implemented with various configurations of charge pump circuits, such as single phase or dual phase charge pumps, and/or doubler, tripler or inverter configurations. The independent charging circuit comprises a parasitic charging capacitor or other voltage source configured with one or more switch devices configured to facilitate charging of the parasitics during any phases of operation of the charge pump circuit. In addition, the independent charging circuit comprises an independent cell, and is local to charge pump circuit for supplying the current for charging the parasitic capacitances, instead of having the current supplied through external bussing or wire bonds.
Furthermore U.S. Patent (U.S. Pat. No. 7,626,445 to Lesso et al.) discloses a dual mode charge-pump circuit and associated method and apparatuses for providing a plurality of output voltages, using a single flying capacitor, the circuit including a network of switches that is operable in a number of different states and a controller for operating said switches in a sequence of the states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage and centered on the voltage at the common terminal, in a first mode and positive and negative output voltages each up to substantially the input voltage in a second mode. and
U. S. Patent (U.S. Pat. No. 7,622,984 to Lesso et al.) discloses a charge pump circuit and associated method and apparatuses for providing a plurality of output voltages using a single flying capacitor. The circuit includes a network of switches that are operable in a number of different states and a controller for operating the switches in a sequence of states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage and centered on the voltage at the common terminal.